Telephone system



Nov. 18, 1941. J..H. voss TELEPHONE SYSTEM Flled June 30, 1939 6 Sheets-Sheet 1 NQE 32 y QW mtwm wk M wuk Kw Q .zbowtu m2:

INVENTOR.

JOHN H V05 3 BY a- ATTORNEYS.

Nov. 18, 1941. J. H. voss TELEPHONE SYSTE M Filed June 30, 1939 6 Sheets-Sheet 3 0mm 73% k QQQQ T m \mwwm MRME v g8. v 3% I oEzeoammm bmmE ES I INVENTOR.

JOHN H VOSS BYM,M

ATTORNEYS.

6 Sheets-Sheet 5 J. H. voss TELEPHONE SYSTEM Filed Ju ne 50, 1959 Nov. 18, 1941.

QQQQ DOW NQ m u 2 5 H Sow oon BYM M,M M ATTORNEYS Nov. 18, 1941. J. H. voss TELEPHONE SYSTEM Filed June 50, 1939 6 Sheets-Sheet 6 INVENTOR. JOHN H V055 BY M M ATTORNEYS Patented Nov. 18, 1941 2,262,824 TELEPHONE SYSTEM John H. Voss, Downers Grove, 111., assignor to Associated Electric Laboratories, Inc., Chicago, 111., a corporation of Delaware Application June 30, 1939, Serial No. 282,037

65 Claims.

The present invention relates to telephone systems and, more particularly, to improvements in the switching apparatus provided in small exchanges of the type adapted for use in rural communities or other areas including only a limited number of subscribers. In providing telephone facilities for the subscribers in an area of this character it is frequently desirable, from the standpoint of installation cost and maintenance, to equip the subscriber substations with ordinary manual type telephones, which may be of the local battery magneto type, and to provide automatic switching facilities in an exchange located in the area, the switches of which are controllable from a remote point, generally the central exchange of a distant city where operators are available at all times. The subscribers lines may be of the single party or multiparty type, or both, and certain of the substations of the system may be of the paystation type. In certain instances it is also economically advantageous to utilize the remotely controlled community automatic exchange as a tandem exchange in setting up connections between the central exchange and a third exchange. Usually the apparatus provided in the remotely controlled community exchange comprises one or more finder-connector links, the

connector portions of which are controllable from the central exchange over one or more trunk lines extending between the community exchange and the central exchange. In those cases Where the traflic requirements are such that a plurality of links must be used, common equipment, including a link distributor, is usually provided for assigning the links to the use of calling ones of the lines terminating at the remotely controlled exchange.

It is an object of the present invention to provide improved switching apparatus of the character described which is of simple and economical arrangement and which may easily be controlled by an operator located at a distant point.

It is another object of the invention to provide an improved arrangement of the character described wherein the apparatus for transmitting incoming call signals and paystation identifying signals to the operators position in the central exchange is partially included in the common equipment of the remotely controlled exchange, thus eliminating the necessity for complicated signal control apparatus in each of the finderconnector links provided in the latter exchange.

It is a further object of the invention to provide apparatus of the character described which 1 is so arranged that the link distributor of the common equipment is held operated until a call routed by way of an assigned link to the operators position in the central exchange is answered, whereby calls originating on the lines terminating at the remotely controlled community exchange must be handled by the distant operator in the order of their initiation, and a'single timing device incorporated in the common equipment may be used for initiating link substitution in the case when the finder portion of an assigned link fails to find the line to which it is assigned and also to release an assigned link in the case when a "call routed to the distant operator's position is not answered within a predetermined time interval.

It is another object of the invention to provide improved apparatus of the character described which is so arranged that when a link in the remotely controlled exchange is seized by the operator in the central exchange a signal is transmitted to the operator only if the connector portion of the link is fully released.

It is another object of the invention to provideyin a-telephone system of the character described, switching apparatus arranged in an improved manner such that a signal of one character is transmitted to the central exchange operator when a link in the remotely controlled exchange is seized provided the apparatus in the remotely controlled exchange is in proper working order, and a signal of different character is transmitted to the central exchange operator if a fault is present in the apparatus embodied in the remotely controlled exchange.

It is another object of the invention to provide, in an automatic telephone system, automatic switching apparatus which is arranged in an improved manner such that when a connection routed by way thereof is released, the apparatus through which the connection is routed is held operated for a time interval during which a busy signal is transmitted over the calling end of the connection.

It is a further object of the invention to provide, in an automatic telephone system, automatic switching apparatus which is arranged in an improved manner such that the ringing control apparatus provided in the connector switch through which a connection is routed is directly controlled by the calling device located at the calling end of theconnection, whereby code ringing may be obtained by selective operation of the calling device. 1 i

It is a still further object of the invention to provide, in an automatic telephone system, an

"control operators position.

improved trunk selecting circuit which is so .ar-

ranged that any one of a plurality of trunk lines may be seized by an automatic switch having access thereto over a single set of outlet contacts included in the switch, thus minimizing the number of contact sets required in the switch to serve a given number of lines.

The features of the invention, as outlined above, are illustratedin their embodiment in a system which comprises a remotely controlled automatic exchange arranged to serve a small number of lines and to function as a tandem exchange between the control or central exchange and a distant manual .office. The automatic switching apparatusof-the remotely controlled exchange comprises a plurality of finderconnector links having trunk lines individual thereto and extending to an operators position in the control oflice, and common equipment including a link distributor for assigning the links links. The common equipment also'inclu'des =a timing device which, in combination with certain of the relays embodied in the common equipment, functions 'to 'cause the distributor to ass'igna new'lirlkto the-useof a calling line in -the-event the-finder portion of the first assigned link "fails to find the calling line 'within "-a predetermined time -interval,-and also to cause an assigned link'to be released in the event a-call "as routed to "the a distant operators position is "not answered within the predetermined time in- "terval. In accordancewith another feature (if "the' inventio'n,eachlink is provided with acir- "cuit including'its associated trunk line for tr-ans- -*mitting to the operators-position a paystation tone signal current in order to 'give' the operator supervision of calls originating at substations -of 'the paystation type. The arrangement is such-that this circuit'isfcompleted when a call originating at a paystation is'answere'd at the The paystation identifying signal, as thus transmitted tofthe control operators position, isterminated a pree determined time interval thereafter through the" provision-of means comprising'a timing device -embodied in the common equipment for interrupting the signal current circuit. The common equipment further comprises apparatus "for par its normal position.

termine the idle or busy condition of such lines. In order that the operator may inform a calling subscriber that a desired called line is occupied with a reverting call without conversing with the calling party after the busy condition of the called line is ascertained, the link circuits are arranged in an improved manner such that the operator may, by simply releasing the connec tion, cause the operated link to be held operated for a predetermined time interval during which a busy tone signal is transmitted from the link over the calling line to inform the calling party that the desired line is busy. More particularly, eachconnector switch is provided with a ringing control relay which is operative to connect the conductors of a selected called line to a source of'ringing current under the control of the operator in the distant exchange. Each link further comprises a timing device, together controlled by the timing-device is also provided for maintaining the 'link operated for a predetermined time interval following the releaseof the connection at the operator spos'ition. During this predetermined time interval the busy 'tonesignal continues, thus informing the calling -subscriber that the desire'd line is'busy. In accordance with another 'feature'of the invention, 'the above-mentioned ringing control relay, as embodied in each link, is operative to connect a selected called line to the ringing current source offthe community exchange for variable time intervals determined byoperation of the calling device provided at the operators position and by means of which theconnector link is directively controlled.

portion --of the Each of the connector switches provided in the remotely controlled exchange is provided with a normal position and is operative to any one of a plurality of positionsto select one of the lines terminating at the exchange. In accordance with a further feature of the invention each link has associated therewith a circuit,'includin the associated control trunk, for transmitting a signal to the central exchange operators position; means being provided in'the link, operative in response to the initiation of a call on the associated control trunk for completingythe circuit portion of the link'occupies The arrangement 'is such that'when the finder switch of the link operates to seize a calling'line, the control apparatus'of only if the connector the link functions to interrupt the signaling cirtially controlling the incoming call signal'lamps 'provided at the operators position and individ- *ually -=-associated ,With the control trunk lines extendingibetween the links of the community "exchange and the operators posit-ion.

Certain of. the subscribers lines terminating "at the communityexchan'ge are or the multiparty type and the arrangement of the automatic "switching apparatus included in the exchange is such that lines of this character are not guarded against incoming calls while occupied with revertingcallsya monitoring operation ofth'e part of the'operator 'being'require'd in order to 'de-- 'cuit just described. In accordance with another feature of the invention an additional signaling arrangement is provided for enabling the'central exchange operator to be'appr'ised at an times as 'to 'thecondition of the apparatus embodied in the remotely controlled exchange.

More particularly, means are provided for normally energizing the above-mentioned signaling-circuits, in-

dividual to the links, with current'having one signaling characteristic, and for energizing the circuits with current/having a difierentsignaling characteristic when a fault is present in the apparatus located in the remotely controlled exchange.

Interoffice callsbetween the central and manual exchanges of the'sy'stem are routed "over-a group of trunk lines extending between the community exchange and the central exchange. The connector portion of each of the finder-connector links located in the community exchange has access to this group of trunk lines. More particularly, the connector switches of the community exchange include corresponding sets of outlet contacts, and each of the switches has access to all of the trunk lines over a single predetermined set of outlet contacts which corresponds to the predetermined contact set in each of the other switches. The trunk lines have associated therewith preselecting apparatus which is operative in response to seizure of any one of the lines by one of the connector switches for selecting another one of the lines for seizure by the other switches, providing an idle one of the lines is available, and operative, when all of the lines are busy, for marking the trunk lines as busy in the predetermined contact sets of the nonoperated a one or ones of the connector switches.

Further features of the invention relate to the particular arrangement of the circuit elements whereby the above and additional operating features are attained.

The novel features believed to be characteristic of the invention are set forth with particularity in the appended claims. The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the specification taken in connection with the accompanying drawings, in which Figures 1 to 6, inclusive, illustrate a telephone system having incorporated therein the features of the invention as briefly outlined above; Fig. '7 illustrates an adapter circuit adapted for use in combination with one of the line circuits shown in Fig. 1; and

' Fig. 8 illustrates the manner of arranging Figs. 1

which is adapted to serve as a tandem exchange between the central exchange and the manual ofi'ice and includes the switching apparatus illustrated in detail in Figs. 1, 2, 3, 5 and 6. This apparatus, in the arrangement illustrated, is

adapted to serve a total of twenty-two trunk and subscribers lines terminating at the community exchange, which lines include the two subscribers lines I0 and II, respectively, and the trunk lines I2, I3 and I4 extending between the community exchange and the manual ofiice 20. The subscribers lines may be of the single party type or the multiparty type, as required. Thus, the lines I0 and II are illustrated as being of the multiparty type, the line I0 having associated therewith two substations A andB and the line II having associated therewith the substations C and D. The indicatedsubstations A, B, C and D are of the local battery, magneto type, a hand generator being provided at each thereof for transmitting alternating current over the associated line.

The automatic switching apparatus provided in the community exchange comprises four finder-connector links, one of which is indicated generally at 30, and common equipment, as illustrated in Fig. 3, which includes a distributor switch for assigning the links to the use of calling ones of the lines terminating at the exchange in a predetermined order. Each of these lines terminates in the exchange in a line circuit,

that associatedwith the subscribers line I0 being indicated generally at I6 and comprising a line relay RI20 and a cut-off relay RI25. vThe line relay RI20 is so constructed that it will operate when its-upper winding is'energized with either direct or' alternating current. Twoadditionalline circuits I1 and I8 are schematically illustrated as being associated with the subscriber's line II and the link line 500, respectively. In order to facilitate a description of the mode of controlling the transmission of paystation signal currents from the links of the community exchange to the distant control operators position 25, the line circuit I6 associated with the subscribers line I0 is illustrated, for purposes of explanation only, as including a paystation signal current transmission circuit.

Each of the finder-connector links provided in the community exchange has associated therewith a trunk line which extends to the operators position 25 in the distant central exchange. Thus, the link 30 includes a repeating coil 393 which terminates one end of a trunk line I5 extending to the trunk circuit apparatus illustrated in Fig; 4 and provided at'the operators position 25. This trunk circuit apparatus comprises a repeating coil 405, one side of which is normally connected to' the conductors of the trunk line I5 and the other side of which is connected to the contact springs of a call and answer jack 400. The trunk circuit apparatus further includes an incomingv call signal lamp 40I, a call and answer key 402 and a dial key 403, all of which are individual to the trunk line I5, and a calling or impulsing device 404 which may be common to the group of trunk lines extending to the operators position 25. There is further included in the trunk circuit apparatus individual to the trunk line I5 a plurality of control relays R420, R430, R440, R450,'-R460 and R410, the first two of which are provided for the purpose of controlling the connection of the impulsing device 404 to the trunk line I5. The remaining four relays are provided in order to control the operation of the signal lamp MI and the operation of the supervisory signal lamp conventionally embodied in the operators cord circuit, not shown.

Referring nowmore particularly to the arrangement of the finder-connector links provided in the remotely controlled communityexchange, the link 30 is illustrated as comprising a finder switch 35 and a-connector switch 40, both. of which are of the well-known rotary type. More specifically, the switch 35 comprises four sets of bank contacts I00 to I03, inclusive,wipers I04 to I01, inclusive, individually associated with the contact' sets, and means comprising a motor magnet I08 and a ratchet and pawl mechanism, not shown, for driving the enumerated wipers over the contacts of their respective associated contact sets. For the purpose of arresting the operation of the finder switch 35, when the wipers of this switch have been operated into engagement with a set of contacts terminating a calling line, there is provided in the finder portion of the link a line test relay RI30. An alternating current relay RI3'I is also provided in the finder portion of the link for the purpose of controlling the supervisory signal lamp embodied in the operators cord circuit to give the operator disconnect supervision in the manner described more fully hereinafter. The connector switch 40, which is similar in construction to the switch 30, comprises five sets of contact --z;an to 2.84,,inclusive, wipers ass to 289, inclusive, individually associated with the genu- :merated contact sets, and means comprising a motor-magnetiloo and a ratchet andpawl :mech- .anism, not shown, fordriving'the enumerated wipers over .the contacts of their:respective associated contact sets. The finder and connector :portions of the link are coupled together for the :transmissionof signal currents therebetween ithrough the provision of a repeating coil M0.

The'relay equipment provided in the connector portion ofrthe link comprises a pair of signal llamp'control vrelaysilFtldll and R145, the first of which is .of the alternating current type, a line Y .or pulsing relay Hi), a slow-acting hold relay Ri55, and a combined lineswitching and link release relay Rllill. This equipment further in? cludes a slow-acting impulse .responsive relay R110, a busytest relay R200, va combined line switching and .digit transfer relay R2I0, a con- .trolprelay R220, and a second digit transfer relay H2311. In order to'select the side of a called 5 line over which ringing current is .to be projected,

there are provided two additional relays R210 .and R215, each of which'is of the two-step type. The" connection of a called line to .the ringing current source conventionally provided in the community exchange is under the control of a these relays, namely, the relay R'330,fin combinationwith the slow-to-operate relay R335,:is pro- 'vided for the purpose of controlling'the operation of the signal lampcontrol'relay Rfli l included in the trunk circuit apparatus'terminating the trunk -1ine.|5 at the operators position 25 and the similar signal lamp control relays individually embodied in the trunk circuits respectively terminating the other trunk lines extending to this operators position. The second. timing device, namely, the pendulum-type relay-R350, in combination with the ,slow-to-operate relay R360, is

provided for measuring the interval during which a :paystation tone signal vis transmitted'to the operators position 25 on a call originating on one of the paystation lines terminating at'thelcommunity exchange. This pair of relays also funcringingcontrol relay R260 which is arranged to be .controlled by a ,slow-to-release impulse responsive relay R250. 'In'order to hold the link operated, under [certain conditiona'for a predetermined time interval after a connection routed Joy way :thereof has' been released at the ,Operators position 25,, there is provided a timing device in the 'form of .a pendulum-type relay R240 which is arranged to control the operation ofia 'sloweto-rele'ase relay R245; The latter relay, in

turn, is. arranged to prevent the completion of certain'release circuits, described more particularly hereinafter, for a predetermined time interval-determined by the operationo-f the-pendulum relay R240. v The'equipment commonly associated with the findereconnector links provided in the community exchange is illustrated in Fig. 3 as comprising the link distributor switchl45 and a timing device 50. More particularly, the distributor switch is of the well-known rotary type and comprises six setsmof contacts 300 to 395, inclusive, of ten points each, wipers 30.6 to 3l'l, inclusive, individually associated'with the enumerated Icontact sets,

and-"means including an operating magnet 3l2 for driving the indicated wipers over the contacts of their respective associated contact sets. The i tions to control the distributor switch in its operation to hunt for an idle link. The common equipment further comprises aneXcha-nge bat tery 5 for supplying current to the various relays and operating magnets, together with a rectifier 394 for maintaining the battery 5 properly charged. Ringing current and the usual busy and dial tone signal currents are supplied by a converter which comprises atransformer .392, and

' This occurs when any one ofthe 'links is seized RA316', a path including, the condenser 398 .for

and is performed in amanner well understood in the art. When operation of the converter is initiated the conductor C391 is grounded to complete an obviouscircuit for energizing'therelay R315. Upon operating, this relay completes, at

' transmitting signalcurrent over the conductor timing device '50 includes a cyclically operative" rotary'switch 3390 which comprises'a single set of contacts, a wiper 39! associated with this con- ,tact set, and a motor magnet 392 for driving the wiper v39l over its associated contacts. Operationof this rotary switch is effected through the provision of a group of cyclically operating relays R365, R310 andRB'lE, each' of which is of the sloW-to-operate type. In order to effect the release of an assigned link a predetermined time interval after'operation thereof is initiated, the rotaryswitch 3951 is arranged to control a pair of cycle counting relays R385 and R380, which relays'are operative in the order named in response to succeeding cycles of operation ofv the indicated rotary switch. The common equipment illustrated in Fig. 3 also includes a start relay R320, a pulsing relay R340, and a pair of additional timing devices inthe form of two pendulumstype relays R338 and R350. The first of T0249. At

RANT, the relay R375 short-circuits its lower winding. The relay R3l5 is so constructed that it will not remain operated when its upper winding is alone energized. Accordingly, it will be apparent that this relay alternately operates and restores periodically to-com plete the above-traced signal current path. In order to control the previously'mentioned cir-' cuits fortransmitting to the central exchange operators position signals indicative of the condition of the apparatus in the remotely controlled exchange, there is "provided a signal control relay R380 which is arranged t be controlled by a battery charge test relay R385. and also by the fuse links, not shown, which are individual to the various current responsive devices included in the switching equipment. r s

As indicated previously, the trunk preselecting apparatus illustrated in Figs. 5-and 6 in associa- 1 .111011 with the interofiice trunk lines l2, l3 and I4, is so arranged that each of the connector switches provided in the community exchange has access to all of the trunk lines by way of a single set of outlet contacts.- To this end, four individual and disconnected link lines 594 to 5211, inclusive, are provided, which lines are individually terminated at corresponding sets of contacts in the four connector switches of the community exchange. Thus, the conductors of the link line 594 are illustrated as'being connected to the respectiveeighth contacts of the contact sets 280, 28I and 233 embodied in the connector switch 40. The remaining three link lines 506 to 501, inclusive, are similarly connected to the respective eighth contacts of the three other connector switches. These four link lines are not multipled together. Since each of the indicated trunk lines is of the two-way type, such that calls may be routed thereover in either direction, provisions are made for rendering these lines accessible to the four finder switches provided in the community exchange. To this end, three link lines 500, 502 and 503, individual to the trunk lines I2, I3 and I4, respectively, are provided which individually extend to line circuits identical in arrangement with the line circuit I6. The line switching operations required incident to the selection and use of the trunk lines I2, I3 and I4 are achieved through the provision of four groups of trunk selecting relays, which groups of relays individually correspond to the four connector switches. The first group of trunk selecting relays, namely, that individual to the link 30, is illustrated as comprising three relays R549, R550 and R560, which individually correspond to the trunk lines I2, I3 and I4, respectively. Similarly, the fourth group of trunk selecting relays, namely, that individual to the fourth link, not shown, comprises the three relays R5I0, R520 and R530, which also individually correspond to the trunk lines I2, I3 and I4, respectively. In order to simplify the disclosure, the groups of trunk selecting relays individual to the second and third links have not been illustrated in the drawings. The groups of trunk selecting relays have commonly associated therewith a group of control relays R600, R6I0, R620, R630, R640, R650 and R660, the first three of which individually correspond to the trunk lines I2, I3 and I4, respectively, and the last three of which also individually correspond to the three trunk lines in the order enumerated The relay R630 is an all-trunks-busy relay and is provided for the purpose of marking the trunk lines as busy in the bank contacts of the nonoperated connector switches when an all busy condition of the trunks I2, I3 and I4 prevails.

Operation of the system Referring now to the operation of the system and considering first a call initiated at the substation A and intended for the substation C associated with the line II, to initiate the call the calling party operates the hand generator provided at the substation A, thereby to project alternating ringing current over the line I0 and through the upper winding of the line relay RI20. When energized by the alternating ringing current, the relay RI20 operates to complete, at RAI2I, an obvious holding circuit for itself. At RAI22, the relay RI20 completes an obvious path for impressing ground potential upon the contact of the contact set I02 which corresponds to the line I0, thereby to mark this line as the calling line in the contacts of the switch 35. At RAI23, the relay RI20 completes a circuit for energizing the distributor start relay R320 in series with the operating magnet 3I2, this circuit extending by way of the grounded all-linksbusy conductor C343, RAI23, the distributor start conductor C3 I4, RA338, the winding of R320, the armature 3I3 and the winding of the magnet 3I2 to battery. Assuming that the wipers of the distributor switch 45 are standing in engagement with the contacts corresponding to the link 30, a branch circuit is also completed for energizing the magnet 290 of the connector switch 40. This branch circuit extends by way of the grounded start conductor C3I4, RA338, the winding of R320, RA325, the wiper 3I0, C344, RAI69, CI94, RA2I9', RA230, the armature 29I and the winding of the magnet 290 to battery. Due to the relatively high resistance of the winding of the relay R320, the magnets 3I2 and 290 are insufficiently energized to operate when this circult is completed. The relay R320, however, operates to complete, at RA32'I, a multiple circuit for energizing its own winding in series with the winding of the magnet 3I2. At RA328, the relay-R320 completes circuits, described hereinafter, for initiating the operation of the timing device 50, At RA326, the relay R320 prepares a circuit, traced hereinafter, for energizing the pendulum-type relay R330 in series with the signal control relay RI45. At RA325, the relay R320 opens a point in the above-traced branch circuit extending through, the Winding of the magnet 290, and prepares a circuit for energizing the pendulum-type relay R350. At RA324, the relay R320 prepares a holding circuit for the link pulsing relay R349. At RA323, the relay R320 prepares a circuit for transmitting paystation tone signal current to the distant operators position 25 and, in so doing, prepares a circuit for energizing the relay R340. At RA322, the relay R320 prepares a holding circuit for the test relay RI30 embodied in the finder portion of the link 30.

At RA32I, the relay R320 completes a circuit for energizing the operating magnet I08 of the finder switch 35, this circuit extending from ground by way of RA32I, RA34I, RA35I, the Wiper 301, C3I'I, RAI36 and the winding of the magnet I03 to battery. When this circuit is completed, the magnet I08 operates to condition the associated ratchet and pawl mechanism to step the wipers I04 to I91, inclusive, one step and attracts its armature I99 to complete the abovementioned circuit for energizing the pulsing relay R349. This latter circuit extends from ground by way of the armature I09, C3I6, the wiper 306,

RA323 and the upper winding of R340 to battery. When energized over this circuit, the relay R340 operates to open, at RA34I, the above-mentioned circuit for energizing the magnet I98, causing this magnet to retract its armature I09 and to release the associated ratchet and pawl mechanism so that thewipers of the switch 35 are stepped one step. When the armature I09 falls back, the above-traced operating circuit for the pulsing relay R340 is interrupted, causing this relay to restore to recomplete, at RA34I, the previously traced circuit for energizing the magnet I08. Accordingly, the magnet I08 is energized and operates to again complete the operating cir-' cuit for the pulsing relay R340 The interrelated operation of the magnet I08 and the relay R340 continues until the wipers of the switch 35 have been advanced into engagement with the set of contacts terminating the calling line I0. More particularly, when the wiper I06 is moved into engagement with the contact having ground po-' tential impressed thereon by the line relay RI20, a circuit is completed for energizing the upper winding of the relay RI30 in series with the lower winding of the pulsing relay R340, this circuit extending from ground by way of RAI22, the wiper I06, the upper winding of RI30, C3I9, the wiper 309, RA352, RA324, and the lower winding of R340 to battery. When its lower winding is energized over this circuit, the relay R340 remains operated independently of its upper winding, thereby tohold the operating circuit for the magnet I08 open at its armature RA34I. Thus, the

step-by-step operation of the finder switch 35 is arrested. When its upper winding is energizedover the circuit just traced, therelay RI30 operates to complete, at the X contacts associated with RAI 33', a holding circuit for itself, this holding circuit extending from ground at RA322 by way of the wiper 308, C3I8, RAI33 and the lower winding of RI30 to battery. Following the completion of this circuit, the relay RI30 completes, at 1RA [33, an obvious path for short-circuiting its upper winding. At RAI3I, the relay RI30 completes a circuit for transmitting a signal current over theestablished calling loop circuit to inform the calling party that the connection has been routed to the operator's position 25. This circuit may partially be traced as extending from one terminal of the dial tone current source, not shown, by way of the condenser 391, C248, RA23 I, CI11, RAI56, RAI3I, CI'IB, RA20I, the condenser 206, RA2I2, CI80, the winding I I3, the condenser H0, the winding II4, CI88 and RA2I1 to the opposite terminal of the dial tone current source. The alternating-character of the current traversing thiscircuit is such that an induced signal volt-. age is developed in the repeater windings I I I and H2, which voltage is reproduced by the receiver provided at the calling substation A. At RAI36, the relay RI30 opens a further point in the operating' circuit for the magnet I08. At RAI3,5, the relay RI30 prepares operating and holding cir-v cuits for certain of the relays embodied in the connector portion of the link. At RAI 32, the relay RI30 completes a circuit, extending by way of the wiper I and the private conductorlflc, for energizing the cut-off relay RI25. The last-men tioned relay, upon operating, interrupts, at RAI 21, the holding circuit for the line relay' RI20. At RAIZB, the relay RI25 opens a point in the operating circuit for the relay RI20, thus disconnecting the. upper winding of the latter relay from across the conductors of the line I0. The relay RI20 now restores to prepare, at RAI22, a further point in the above-mentioned circuit for transmitting paystation tone signal current to the operators position 25. At RAI23, the relay opens the above-traced path" for impressing ground potential upon the start conductor C3I4,

, thereby to interrupt the operating circuit for the relay R320.

The relay RI30, upon operating, also completes the above-mentioned circuit for energizing the upper winding of the signal control relay RI45 in series with the pendulum relay R330, this circuit extending from ground at RA326 by way of the Winding of R330, RA336, the wiper 3, C345, RAI34 and the upper winding of RI4 5 to battery. When energized over this circuit, the relay RI45 operates to prepare, at RAI41, a, path for short-, circuiting its lower winding and to interrupt, at RAI4.1', a point in the normally completed circuit for energizing the signal lamp control relay R460 included in the trunk circuit apparatus associated with the trunk line I5 and provided at the operator's position '25. This circuit, over which the relay R460 is normally energized, extends from ground by way of the repeater winding 391, the conductor I511, R A432, the repeater Winding 400, the winding oi R450, the winding of R450, the winding 401, RA434, the conductor I51), the winding 306;, 03.4.0, the resistor I43, RAM? and the lower winding of RI 50 to battery. The resistance normally ,included in this circuit is such that the relay R460 is theonly one of the relays energized thereover which is normally operated. When, however, the-relay R145 operates to interrupt this circuit, the relay R460 is deenergized and restores to complete a circuit .for energizing the relay R410, the latter circuit extending from ground by way of RA42I, RA435, RA45I, RA46I and the winding of R410 to battery. When energized over this circuit, the relay R410 operates to complete, at ,RA413, an obvious holding circuit for itself and to complete, at RA41I, an obvious circuit for energizing the incoming call signal lamp 40L At RA412, the relay R410 opens a point in a supervisory circuit which is adapted to extend through the contacts of the jack 400 to the operators cord circuit. The energization of the lamp 40I serves to signal the operator on duty at the operators position 25 that an incoming call is present upon the trunk line I5 which should be answered.

When the above-traced circuit is completed for energizing the upper winding of the relay RI45 in series with the pendulum relay R330, the latter relay is also caused to operate. The relay R330 attracts its armature-RA332 into engagement with the associated weighted armature 33 I, thereby to initiate vibration of the latter armature in the usual manner, and momentarily to complete an obvious operating circuit for the slow-to-operate relay R335. During vibration of the armature 33! the periods of engagement between this armature and RA3-32 are insuflicient to cause the operation of the sloW-to-operate relay R335. Thus, the relay R330 functions as a timing device to prevent, for a predetermined time interval following its initial energization, the operation of the relay R335. When vibration of the armature 331 is substantially terminated, the operating circuit for the relay R335 is held completed, and the latter relay operates to complete, at RA331, an obvious holding circuit for itself. At RA338, the relay R335 opens a further point in the previously traced operating circuit for, the relay R320. At RA336, the relay R335 interrupts the abovetraced series circuit including the winding of the relay R330 and the upper winding of the relay RI45, causing both of these relays to restore. The restoration of the relay R330 is without effect. The relay RI45, upon restoring, recompletes the above-traced circuit for energizing the lower winding of the relay RI 50 in series with the respective windings ,ofthe relays R450 and R400, thereby to cause the reoperation of the lastmentioned relay. Upon reoperating, the relay R460 functions to open, at RA46I, a point in the previously traced operating circuit for the relay R410. Following the reoperation of the relay R460 no further operation of the apparatus occurs until the call is answered at the operators position 25.

In the event the finder portion of the link 30 fails to find the calling line I0, the timing device 50 provided in the distributor functions to initiate the release of the assigned link and to cause a second link to be assigned to the use of the calling line. This timing device also functions to initiate the release of the link in the event the call is forwarded to the operators position 25 and is not answered within a predetermined time interval. Operation of the timing device 50 is initiated in response to operation of the distributor start relay R320. More particularly, when the start relay R320 operates, a circuit is completed for energizing the slow-toe operate relay R355, this circuit extending from ground by way of RA328, the winding of R365, and the resistor 356 to battery. When energized over this circuit, the relay R305 operates to open, at RA3B1, the path normally short-circuitingthe winding of the relay R310, permitting the latter relay to be energized in series with the resistor 314. Shortly thereafter, the relay R310 operates to open, at RA31I, a point in the path normally short-circuiting the winding of the third slowto-ope'rate relay R315, permitting the latter relay to be energized in series with the resistor 318. When the relay R315 operates, it functions to short-circuit, at RA315, the winding of the first slow-to-operate relay R365. Thus, the relays R365, R310 and R315 are caused sequentially to operate and then sequentially to restore. During each cycle of operation of these three relays, a circuit is completed for energizing the operating magnet 392 of the rotary switch 390. More specifically, this circuit is completed each time the relay R310 operates and extends from ground at RA328 by way of RA312 and the winding of the magnet 392 to battery. This circuit is also interrupted, at RA312, each time the three slowto-operate relays are caused to restore. Each time the magnet 392 is energized and deenergized, it functions to step the wiper 39E one step, so that, after a predetermined number of cycles of operation of the three slow-to-operate relays, the wiper 39! is advanced into engagement with its associated tenth contact. Thereafter, and during the interval of the next cycle of operation of the three slow-to-operate relays when the relays R310 and R315 are concurrently operated, a

circuit is completed for energizing the relay R385, this circuit extending from ground by way of RA313, RA311, the wiper 39! and its associated tenth contact, and the winding of R385 to battery. When energized over this circuit, the relay R385 operates to complete, at RA381, an obvious holding circuit for itself and to prepare, at RA386, a circuit for energizing the relay R380. Following the operation of the relay R305, the three relays R355, R310 and R315 and the rotary switch 390 continue to operate until the wiper 39! is advanced into engagement with its associated ninth contact. While in engagement with this contact and during the interval when the two relays R310 and R315 are concurrently operated, the circuit is completed for energizing the relay R380, this circuit extending from ground by way of RA313, RA311, the wiper 30! and its associated ninth contact, RA3B5, and the winding of R380 to battery. The relay R330, upon operating, completes, at RA382, an obvious holding circuit for itself and prepares, at RABHi, a circuit for energizing the operating magnet 3i2 of the distributor switch 45. Following the operation of the relay R380, the three cyclically operating slow-to-operate relays and the rotary switch 390 continue to operate until the wiper 39! is advanced into engagement with its associated eighth contact. While standing in engagement with this contact, the above-mentioned circuit is completed for energizing the magnet 3!2 during the interval when the relays R310 and R315 are concurrently operated. This circuit extends from ground at RA313 by way of RA311, the wiper 39! and its associated eighth contact, RA30!, and the winding of the magnet 3!2 to battery. When this circuit is completed, the winding of the start relay R320 is obviously short-circuited. The magnet 3l2, when energized over the circuit just traced, operates to condition its associated ratchet and pawl mechanism to step the wiper of the distributor switch 45 one step. Shortly thereafter the relay R310 releases to open at RA313, the operating circuit for the magnet 3!2. When the magnet 3l2 is thus deenergized, the ratchet and pawl mechanism associated therewith operates to advance the wipers of the switch 45 one step. Thus, the wipers 306 to 3! I, inclusive, are advanced out of engagement with the contacts terminating the control conductors individual to the link 30 and into engagement with the contacts terminating the control conductors individual to the next succeeding link. When the winding of the. start relay R320 is short-circuited in response to the completion of the above-traced operating circuit for the magnet 3!2, this relay restores to open the previously traced operating and holding circuits for the relays R330, R335, R330, R355, R310, R315, R380 and R385 included in the distributor, causing the operated ones of these relays to restore. In addition, if the call has been forwarded to the operators position 25 but has not been answered thereat within the time interval required for the timing device 50 to complete its operation, the previously traced holding circuit for the relay R!30 is interrupted at RA322. At RA32I, the relay R320, upon restoring, opens a point in the previously traced circuit for energizing the operating magnet I08 of the switch 35, thereby to .deenergize this magnet if operated. If operated at the time the start relay R320 restores, the relay R!30, upon restoring, functions to open, at RAI32, the operating circuit for the cut-off relay R!25, causing the latter relay to restore to reprepare the operating circuit for the line relay R!20.

In the event the link selected by the distributor switch 45, upon the first step taken thereby, is busy at the time it is selected, the guard conductor individual thereto and corresponding to the guard conductor C344 individual to the link 30, is connected to ground. Ground potential is also present upon the five contacts of the contact set 304 which do not correspond to links in use, these five contacts being multipled together and permanently grounded. An alternative circuit is, therefore, completed for energizing the distributor switch operating magnet 3!2, this circuit extending by way of the grounded guard conductor of the selected link, the wiper 3!0, RA325, the armature 3!3 and the winding of the magnet 3!2 to battery. The completion of this path also results in the continued short-circuit ing of the start relay R320, providing ground potential is present upon the distributor start conductor C3!4. In this regard it is pointed out that ground potential is maintained upon the start conductor C3!4 by the relay R!20 if the operation of the distributor is caused by failure of the finder switch 35 to find the calling line I0. Ground potential will also be applied to this conductor if another calling line is waiting for the assignment of a link thereto. In either case, the

distributor start relay R320 is prevented from reoperating until an idle link is selected. When the magnet 3l2 is energized over the alternative circuit just traced, it operates to condition the associated ratchet and pawl mechanism to step the wipers 306 to 3! I, inclusive, a second step and to interrupt, at its armature 3!3, a point in its alternative operating circuit. Accordingly, the wipers of the distributor switch 45 are advanced a second step or into engagement with.

another set of contacts. If this other contact is available for energizing the magnet 3l2 due to the absence of ground potential upon the guard conductor corresponding to the idle link.- Accordingly, the stepping operation of the distributor switch is arrested and the path, including the 'wiper 3|0 and RA325, for short-circuiting the winding of the relay R320 is interrupted. Accordingly, the start relay R320 is permitted to reoperate to initiate the operation of the finder switch of the selected link to search for the calling line in the exact manner just explained with reference to the finder switch 35. In this regard, it will be apparent that if the operation of the distributor resulting from operation of the timing device 50 is due to failure of the finder switch 30 to find the calling line I0, the cut-off relay R|25 is not caused to operate and hence the line relay R| is operated when the second link is selected. Accordingly, when the second link is found and the short circuit across the distributor start relay R320 is opened, this start relay is energized and operates to initiate the operation of the finder portion of the second link to search for the line 10. If, on the other hand, the calling line I0 is found by the finder switch 35 and the call is forwarded to the operators position 25, but the operator fails to answer the call within the time required for the timing device 50 to complete its operation, the finder switch of the second link is not started in operation to search for the calling line l0.

' Thisfis true for the reason that when the finder switch 35 finds the calling line [-0, the cut-off relay vEH operates to cause the restoration of the line, relay Rl20 and this line relay will not reoperate unless ringing current is again projected over the line l0. During the sequence of operations just described, however, and when the relay Rl restores in response to the release of' the distributor start relay R320, the

above-traced circuit over which signal current'zis transmitted to the calling substation is interrupted at RA=I3 l. Hence, the signal being transmitted to the calling party is terminated.

Accordingly, the calling party is informed that the call :has failed and may reinitiate the call by zby againoperating the hand generator provided at the calling substation.

Continuing now with the operation of the ap- V paratus to extend the connection to the desired .calledsubstation C, it: is pointed out that to answer the call the operator attending the position 25 first inserts the plug terminating her :cord circuit in thecall and answer jack 400 and thereafter momentarily operates the call and answer key 40 2 to its ofir-norlmal position. When the operator inserts the plug terminating her :cord circuit in the jack 40.0, ground potential is impressed upon the sleeve contact of this jack in the usual manner. Accordingly, when the key 402 is operated to its off-normal position to close "the contact springs 412, an obvious circuit is completed for energizing the relay R440. This relay, upon operating, completes, at RA4'43, an

operated after the key 402 is released and allowed to return to its normal position. At RA44I the relay R440 opens the circuit for energizing the signal lamp 40L At RA444, the relay R440 interrupts the holding circuit for the relay R470, causing the latter relay to restore and open, at RA47I, a further point in the circuit for energizing the signal lamp 40!. At RA442, the relay R440 completes a path for short-circuiting the high resistance winding of the relay R460, thereby to exclude the winding of the latter relay from the previously traced series circuit including the winding of the relay R450 and the lower winding of the relay RI50. As a result, the marginal relays R450 and RI50 both operate, the first-mentioned thereof functioning to open, at RAl, a point in the previously traced operating circuit for the relay R470 before the relay R460 restores. The relay Rl50, upon operating, prepares, at RAl52, the above-mentioned path for short-circuiting the lower winding of the relay Rl45. At RAI53, the relay R| prepares an alternative circuit, traced hereinafter, for nergizing the upper winding, of the relay Rl45.

At RAISI, the relay Rl50 completes a circuit for energizing the slow-acting relay Rl55, this circuit extending from ground by way of the wiper 287, 010i, RAl5lvand the winding of Rl to battery. The relay Rl55, upon operating, completes, at RAI 57, an obvious circuit for energizing the relay Rl and prepares, at RAI58, holding circuits, traced hereinafter, for the two relays R270 and R275. At RAI56, the relay RI55 interrupts the previously traced circuit for conducting signal current through the windings H3 and l M of the repeater I I0, thereby to terminate the signal being transmitted to the calling party. At RAI56 and its associated working contact, the relay EH55 prepares a further point in the previously mentioned circuit for transmitting paystation tone signal current to the operators position 25,

The relay Ri50, upon operating, prepares, at

RAiGIl, an alternative circuit for energizing the, relay Rliiil and completes, at RAI64, an obvious multiple holding circuit for the relay Rl55. At RAISE, the relay R160 prepares a circuit, traced hereinafter, for energizing the operating magnet 290 of the rotary switch 40. At RAIGB, the relay Rl60 prepares a circuit for'energizing the slowacting pulse responsive relay RITE). At RAIG'I, the relay RI60 connects multiple ground to the release conductor CIEH. At RAI68, the relay R4 60 completes a multiple holding circuit for the obvious holding circuit for itself so that itis-held relay R130, this circuit extending from'ground by way of'RAi68, RA'I33' and the lower winding of R430 to battery. At RAISS', the relay RIB!) opens one of the paths for impressing ground potential upon the all-links-busy conductor C343. At RAifie, the relay R'l00 opens a point in the circuit, traced hereinafter, for energizingthe magnet 290 during the release of the link, and completes an obvious path for impressing ground potential upon the link guard conductor C344 individual to the link 30. When this guard conductor is grounded a circuit is completed for energizing the pendulum relay R350, this circuit extending by Way of the grounded conductor C344, the wiper 3E0, RA325 and the winding of R350 to battery. At its armatures RAEBZ and RA] 67, the relay El 60 connects the link line conductors C3 38 and Cfi ll to the link line conductors Clilii and C338, thereby to complete a talking circuit, including the three repeating coils H0, .393, and 405 between the calling substation tion tone circuit associated with the line I is illustrated in its association with this linefor purposes of explanation only. In the present case, one loop of this circuit may. be traced as extending from one terminal of the paystation tone current source, not shown, by way of Cl24; the condenser I19, RAIZZ; the-wiper I06", RAI33,

C3l9,.the wiper 309, the condenser342, RA323,

the wiper 306, C3l6, RAISE, RAI3I, CH8, RA20I, the condenser 206, RA2I2, RA2-32, CH9, RAl62, C348,- the two windings 394'and 305, thescondenser 395, C341, RANT, RAI14, Cl89, RA231 and RA2|1 to the opposite terminal of the pay-- station tone current source. Due to the alternating character of the current traversing this circuit, induced voltages are developed in the repeater windings 396 and'39'l which cause current to traverse the loop including the trunk line conductors 5a and IEb and the windings 406 and 40-! of the repeating coil 405. This current is transmitted through the repeating coil 405 to the receiver of the: operators telephone set, thereby tosignal-the operator that the call originates' at a substation of the paystation type.

When the relay R350 is energized over the above-traced circuit, it attracts its armature RA355" into engagement with the weighted armature 354, thereby to'initiat'e vibratory movement of the latter armature. After a predetermined time interval, during which the armatures 354- and'RA355 are only intermittently engaged, the

vibration of the armature 354 ceases and this armature settles into engagement with the armature RA355 to complete an obvious circuit for energizing the slow-to-operate relay R360; Upon operating, the relay R360 completes, at RA36I, a circuit for energizing the distributor operating magnet 3H and, in so doing, short-circuits the winding of the distributor start relay R320. The

circuit for energizing the magnet 3l2 extendsfrom ground at RA3SI by way of RA353 and the winding of the mag-net 312 to battery. When energized over this circuit, the magnet 312 operates to condition the associated ratchet and pawl mechanism tostep the wipers of the switch 45 one step andto open, at its armature 3l3, a point in the previously traced holding circuit for the relay R320. The relay R320 restores when its the operatorsposition 25. The relay R350, upon.-

restoring, interrupts, at RA355 and its associated armature 354, the operating circuit for the.

relay R350 and opens, at RA353, a point in the above-traced circuit for energizing the magnet- 3l2, whereby the ratchet and pawl mechanism associated with this magnet ispermitted to operate and advance the wipers of the distributor switch 45 into engagement with the contact set terminating the control conductors individual to the next link. From this point on the distributor switch 45 is caused to operate. step by step Concur- Thus, the operation of in the manner previously explained until anidle link is found, providing an idlelink 'is available. During such movement of the distributor switch Wipers, ground potential is maintained upon theupper winding terminal of the start relay R320 so that this relay is prevented from operating In the event-all of the links are busy, the step by-step operation of the distributor switch 45- continues until the wipers of this-switch are op-' erated into engagement with their respectiveassociated. last contacts.

connected to the last contact of the contact-set 304, which contact set terminates the guard con-- ductors individual to the various links. So l0ng as any link is idle, ground potential is maintained upon the indicated all-links-busy con-- ductor. Thus, so long as the link 30-is idle, a path extending from ground by way of RA238, CI93 and RAIBB is held completed for maintaining ground potential upon the conductor C343. This path is interrupted at RAIG8' in response to operation of the relay-Rl00., when'the call routedthrough the link 30 is answered at the operators position 25. Similar multiple paths extending through the contacts of the con trol relays embodied in the other links are provided, so that ground potential is present upon the conductor 0343 so long as any links isidle. Hence, during a hunting operation of the distributor switch 45 the last contact of the contact set 304- is grounded, indicating a busy link, so

that the stepping operation of the switch is not.

arrested and movement of the switch wipers may continue until the idle link is located. When, however, all of the links become busy, all of the above-mentioned multiple paths are interrupted and ground potential is removed from the conductor 0343. Accordingly, when the wiper 3I0 is moved into engagement with the contact terminating this conductor, no further circuit is available for energizing the magnet 3l2- and the stepping operation of the distributor switch 45 is' arrested. If a call is initiated on one ofv the lines terminating at the community exchange at a time when all of the links are busy, the operation of the line relay associated with. the calling line causes the winding of the distributor start relay R320 to be short-circuited. Thus, if a call is initiated on the line 0 at a time when all of the links are busy, the line. relay RI20, upon operating, short-circuits the winding of the relay R320 over a path extending from the lower terminal of this winding by way of RA338, (13M RAI23, C343, the wiper 3l0 and RA325 to the upper terminal of the relay R320. In such case, however, the line relay individual. to the calling line is locked in its energized position so that when a link thereafter becomes available, the link is assigned to the use of the calling line and the call is forwarded to the operators position 25 in the manner set forth above. Thus, from the preceding description, it-will be apparentthat when a call is initiated on the line 10, to cause the In this regard, it will be. noted that the all-links-busy conductor C343- is:

operation of the line relay RI20, this relayis locked energized over a circuit including its lower winding and is not deenergized until the cut-off relay Rl subsequently operates in response to operation of oneof the finder switches to seize the line l0. When the all-busy condition of the links is terminated, through the release of one of the links, the path controlled by the relays of this link for impressing ground potential upon the all-links-busy conductor C343 is recompleted. Accordingly, the magnet 3| 2 is again energized and the stepping operation of the switch is initiated. until the idle link is found, at which time the absence of ground potential from the guard conductor individual to the idle link causes the deenergization of the magnet 3I2. When the wiper 3| 0 is moved out of engagement with its associated last contact, the above-traced path for short-circuiting the winding of the distributor start relay R320 is interrupted. However, ground potential is maintained upon the upper winding terminal of this relay over a path extending by way of the wiper 3|0 and RA325 to maintain the relay short-circuited so long as the distributor switch wipers are being stepped over contacts corresponding to busy links and until the idle link is located. When the idle link is found, the stepping operation of the switch 45 is arrested and the relay R320 is conditioned to operate. Thus; the selected idle link is conditioned for use in extending another call to the operators position 25.

After the talking circuit between the substation A and the operators telephone set has been established in the manner described above, thecalling party to ring the desired substation, monitor the connection until the call is answered, and then release the operated link in the manner described in detail hereinafter. Alternatively, if the operator, upon answering the call, ascertains from the ringing operation being performed at the calling substation that another substation associated with the line I0 is being called, she may wait until the ringing operation is ended and release the operated link. If the calling line I0'is arranged for divided code ringing, the call may be intended for a substation associated with this line which has its ringer connected to the side of the line opposite the side of the line to which the ringer provided at the calling substation is connected. In such case the operator instructs the calling party to hang up and then releases the operated link. The operator next initiates a call to the line I0 by seizing one of the available links and dialing the directory number designating the desired substation. The calling subscriber after waiting a reasonable time interval, during which the call may be routed to the desired substation, again removes his receiver from its supporting hook, thereby to complete the desired talking circuit,

, assuming the call has been answered at the called substation. The operator, after monitoring the connection to see that the call is answered may release the operated link. It will be noted that This stepping operation continues when the connection is released at the operators 7 position, all of the line equipment associated with the line I0 is released. Accordingly, this line is not guarded against seizure when occupied with reverting calls.

In the present case, wherein the call initiated at the substation A is intended for the substation C associated with the line H, the operator, upon ascertaining the identity of the called substation, operates the dial key 403 and dials the directory number designating the called substation. When the dial key 403 is operated to its off-normal position, the springs 0 are closed to complete a circuit, extending by Way of the grounded sleeve contact of the jack 400, for energizing the sloW-to-release relay R420. At the springs 4H, a parallel circuit is completed for energizing the relay R430. The relay R420, upon operating, opens, at RA42I, a further point in the previously traced circuit for energizing the signal lamp control relay R410. The relay R430, upon operating, opens, at RA43'5, a further point in the last-mentioned circuit. At its armatures RA43| to RA434, inclusive, the relay R430 disconnects the conductors of the trunk line [5 from the windings of the repeating coil 405 and connects these conductors to the pulsing springs of the calling or impulsing device 404. Thus, two points are opened in the previously traced circuit for energizing the relay R450 in series 'with the relay R|50, and an alternative low resistance circuit including the pulsing springs of the calling device 404 is completed for maintaining the last-mentioned relay operated. The relay R450, upon restoring, reprepares, at RA45I, the operating circuit for the relay R410. With the relay R430 operated, a pulse train comprising one or more impulses is transmitted over the trunk line IE to the line or pulsing relay R|50 included in the operated link 30 each time the dial of the calling device 404 is moved off normal and then released. The number of impulses in each train is, of course, determined by the numerical value of the digit dialed. In this regard, it is pointed out that the lines terminating in the connector switch 40 are divided into three groups, the first eight contact sets being utilized to terminate a group of eight lines, the ninth set of contact points being reserved as the starting position for the selection of lines in the second group, the contact points numbered from l0 to IT, inclusive, being utilized to terminate the conductors of the lines in the second group, the eighteenth contact set being reserved as the starting position for the selection of lines in the third group, and the contact points numbered from l9 to 24, inclusive, being utilized to terminate the conductors of the lines forming the third group. The twenty-fifth set of contacts in the rotary switch 40 represents the home or normal position of this switch, a position which is occupied by the wipers of the switch when the link 30 is idle. It will be apparent, therefore, that in order to select a called line of the first group a single digit of the numerical value designating the called line must be dialed at the operators position. To select a line of the second group a first digit of nine impulses followed by a second digit designating the desired line must be dialed. To select a line of the third group a first digit of nine impulses, a second digit of nine impulses and a third digit of the numerical value designating the line are required to cause the connector switch 40 to operate to the desired line. In the present case, wherein the called line H is the fourth line of the sec'ond group, the line selecting digits whichthe operator mustdial in order't'o select this line" comprise a first digit of nine impulses, followed by a second digit of four impulses.

During each impulse of the first digit dialed at the operators position, the impulsing springs of the calling device 404 are opened to interrupt the circuit over which the pulsing relay Rl50 is being held energized. This relay, upon restoring at the beginning of the first impulse of the first digit, completes a circuit for energizing the slow-acting relay RI10 in multiple with the operating magnet 290 of the rotary switch 40,

one branch of this circuit extending from ground by way of'R'AI64, RAII, RAI'SB and thewinding of R110 to battery, and the other branch extending by way of RAIN, RlAl5l, RAI65, C184;

RA202, RA2I4, RA233 and the winding of the magnet 290 to battery. At RAIBI, the relay RI'50 also opens a point in the operating and holding circuits for the relay R155. The latter relay, due to its slow-to-release characteristic, remains operated during impulsing.

I When energized at the beginning of the first impulse of the first digit, the relay R110 op'erates to complete, at RAI12, a circuit for energizing the relay R220, this circuit extending from ground by way of RAI12, Cl85, RA204, RA2 I5 and theupper winding of R220 to battery. At

RAI13, the relay R110 preparesa circuit, traced Asindicated above, each time the line relay RI50 restores and reoperates in response to an impulse transmitted thereto over the trunk line l5, it functions to complete and then interrupt theabove-t'raced circuit for energizing the magnet 290. Each time this'magnet is energized and then deenergized, it operates to advance the wipers 285 to 289, inclusive, one step. Accordingly, at the end of the first digit of impulses, the indicated wipers are left standing in engagement with the contacts corresponding tothe numerical value of the digit. When the wipers of the switch 40 are stepped to their respective-first offnormal positions a multiple path is completedfor impressing'ground potential upon the guard conductor C344, this path extending from ground by way of the wiper 281 and the multipled" first to twenty-fourth contacts of the contact set: 282 to the conductor C344. When the wiper 281 is moved off normal a point is also opened in the previously traced operating circuit for therelay' Rl55. In the present case, wherein a first digit of nine impulses is dialed, the wipers of the switch 40 are advanced into engagement with:

digit and during the interdigit'pause'between the.

first and second digits. Inthis regard, it will be understood that the interdigit pause, during which the line relay Rl50 remains operated, is' of suflicient length to permit the release of the two relays R|10 and R220 in the order named.

At the beginning of the second digit, the redigit the wipers of the switch 40 are also" advanced at the'rate of one step for each impulse of the digit. In the'present case, wherein a second digit of four impulses is dialed, the wipers 285 to 209, inclusive, are" left standing in engagement with their respective associated thirteenthcontacts, i. e.-, the contacts terminating the conductors of the called line I I, at the conclusion of the" digit. Shortly following the end of the second digit and when the relays RI" and R220 sequentially restore, a circuitis completed, at RA222, for energizing the digit'transfer relay R230, this circuit extending from ground at RAIGT by way of CISI, the wiper 289 and' its associated thirteenth contact, RA2I8, RA2-22' and the winding of R230 tobattery. When energized over this circuit, the'relay R230 operates to open, at RA23I- and its associated' resting contact, a further point in the abovetraced circuit for projecting signal current over the calling line. At RA23I and its associated Working contact, the relay R230 prepares a circuit,- traced'herein'after, for projecting busy tone current over the calling line. At RA232' and RA2'31, the relay R230 opens the multiple connections between the linkline conductors C| andCI08'and' the'link line conductors C348 and C341. At RA233, the relay R230 opens a point in theabove traced circuit for energizing the magnet2'90 and prepares a circuit'for energizing the relays R210 and R215 in accordance with the im-- pulses of the third digit. At RA234, the relay R230-prepares a circuit for energizingthe pendulum relay R240. At RA2'35, the relay R230 completes an obvious path for short-circuiting the lower winding of the' relay R220, thereby'to render thelatter relay slow to release. At RA236, the relay R230- prepares a circuit for energizing the" slow-to-release relay R245; At RA231', the relay R230completes a holding circuitfor itself, this holding circuitextending by way of the grounded release conductor CNN, the wiper 280" and itsassociated thirteenth contact; RA263,

side'ofa selected" called line ringing current is to" be'project'edi Thus, ifthe' line H isarranged for divided ringing, such that the ringers provided at certain" of the substations associated therewith are connected between one side of the line and groundi while the ringers provided at the other substations associated with the line are connected between the other side of the line and ground, it is necessary, in order to signal the called subscriber, to project ringing current of the proper code over the side of the line to which the'ringer provided atthe desired substation is connected. The two relays R210 and R21'5 are: so: arranged that with the relay R215 restored; ringing: current is projected" over the negative: side of a selected called line, Whereas if the relay R2-15=is operated, ringing current is projected over the positive side ofaselected lays Rl ln and R220 are caused to' reoperate in the exact manner described above. During this the relay R210.

called line. In order to cause the operationiof' the relay R210 without energizing the relay R215 a third digit of one impulse must be dialed at the operators. position 25. R210 and R215 are to be operated, a third digit of two impulses must be dialed. Hence; if the ringer provided at the desired substation C is connected between the positive line conductor l lb and ground, the third digit dialed at the operators position 25 will comprise two impulses. At the beginning of the first impulse, when the relay Rl50 restores, the previously traced circuit is completed for energizing the relay Rl10, which latter relay reoperates to cause the reoperationof the relay R220 and to perform the other functions previously described. A branch of this circuit is completed through the upper winding of This branch circuit extends from ground at RAI64 by way of RAII, RAI65, CI84,RA202, RA2I 4, RA233, RA212 and its associated upper contact, and the upper windingof R210 to battery. When energized over this circuit, the relay R210 partially operates to complete, at the X contacts associated with RA213, a path for short-circuiting its lower winding, this path extending from ground at RAI64 by way of RAI5I, RAI65, Cl84, RA202, RA2I4, RA233, RA212, the lower winding of R210, RA213, Cl81 and RAl5B back to ground. At the end of the open-circuit period of the first impulse, when the line relay R|50 reoperates, the short-circuiting path just traced is interrupted at RAI5I, permitting the two windings of the relay R210 to be energized inseries. When this occurs, the relay R210 completes its operation to prepare, at RA21I, a point in the circuit for energizing the busy test relay R200 and to prepare, at RA214, a circuit for energizing the relay R2I0. At RA212 and its' associated upper contact, the relay R210 opens a point in its own operating circuit. At RA212 and its associated working contact, the relay R210 prepares a point in the operating circuit for the relay R215. At the beginning of the open-circuit period of the second impulse, when the line relay R150 again restores, the upper winding of the relay R215 is energized over the pulsing circuit which may now be traced as extending from ground at RA|64 by way of RAI5 I, RAI65, C184, RA202, RA2I4, RA233, RA212 and its associated working contact, RA211 and the upper winding of R215 to battery. When its upper winding is energized over this circuit, the relay R215 partially operates to complete, at the X contacts associated with RA218, apath extendingby way of the grounded conductor C181 for short-circuiting its lower winding. At the end of the open-circuit period of the second impulse, this short-circuiting path isinterrupted, permitting the two windings of the relay R215 to be energized in series. When this occurs, the relay R215 completes its operation to prepare, at RA216 and RA219, a circuit, traced hereinafter, for projecting ringing current over the positive side of the selected line I l.

Shortly following the end of the third digit, the relay R| restores in the manner previously explained. Upon restoring, this relay interrupts the operating circuit for the relay R220 and completes, at RAI1I, the above-traced test circuit including the upper winding of the busy test relay R200. In this regard, it is pointed out that if the selected line H is busy, ground potential is present upon the private conductor c thereof. Accordingly, the busy test relay is energized over the test circuit, this circuit extending by way If both of the relays of the grounded conductor 0, the thirteenth contact ofthe set 280, the wiper 285, RA21I,

R2l0. At RA202, the relay R200 opens a point in the above-traced pulsing circuit extending to the two relays R210 and R215, and prepares a circuit for energizing the relay R240. Shortly followingthe operation of. the relay R200, the relay R220 restores to open at RA22I, a point in the operating circuit for R200, and to prepare, at RA223,

the operating circuit for the relay R2 l 0.

The relay R200, upon operating, also completes, at RA20I, the above-mentioned circuit for transmitting busy tone signal current to the calling subscriber and a branch circuit for transmitting the busy tone signal current to the telephone instrument embodied in the operators cord. circuit. The first of these circuits extends from one terminal of the busy tone current source by way of the intermittently operating armature RA316','the condenser 398, C249, RA20I, the condenser 206, RA2I2, Cl80, the windin N3, the condenser H9, the winding H4, Cl88 and RA211 to the opposite terminal of the busy tone current source. Due to the alternating character of this current, a corresponding induced voltage is developed'in the windings Ill and H2 which causes the usual busy tone signal to be reproduced by the receiver of the telephone instrument provided at the calling substation A. The branch circuit traversed by the busy tone current extends from. one terminal of the busy tone current source by way of the intermittently operating armature RA316, the condenser 398, C249, RA20l thecondenser 206, RA2I2, RA2I3, RA26I, Cl19, RAI62, C348, the windings 394 and 395, the condenser 395 ',.C341, RAIG'I, RAIN Cl89, RA262, RA2I6 and RA2I1 to the opposite terminal of the busy tone current source. The induced voltage developed in the windings 396 and 391 of the repeatingcoil 393 causes the operation of the receiver embodied in the operators cord circuit, thereby to signal the operator that the called line is busy. In this regard, it is pointed out that the operator, after dialing the line selecting digits and the digit designating the side of the line over which ringing current is to be projected, restores the dial key 403 to normal to cause the restoration of the relay R430, the reoperation of the relay R450 and the release of the relay R420 in the order named. Thus, the impulsing device 404 is disconnected from the trunk line l5 and the conductors of this trunk line are extended to the repeating coil 405. In other words, when the key 403 is restored to normal,

- the signaling channel between the operators tel- R110 restores at the end of the third digit :to complete the above-traced test circuit including the upper winding of the relay R200, the busy test relay is not energized and remains in its restored position. storing, also functions, in the manner previously explained, to open the operating circuit for the relay R220. Shortly thereafter, the relay R220 restores to open, at RA221, apoint in the abovetracted test circuit and to complete, at RA223, the operating circuit for the relay R210. The last-mentioned circuit extends from ground at RA161' by way of C191, RA214, RA223, RA205 and the winding of R210 to battery, Upon operating, the relay R210 completes, at RA21 1,, a path extending by way of the wiper 285 for impressing ground potential upon the private conductor c of the called line 11, thereby to mark this line as busy in the bank contacts of the other connector switches having access thereto. When ground potential is impressed upon the conductor 0, the cut-ofi relay embodied in the line circuit 11 operates to disconnect the operating winding of the line relay included in this circuit from across the conductors 11a and 11b;

The relay R110, upon rebe interfered with. If the operator :ascertains that the ;called line is busy, ,she may cause .busy tone current to be returned to the callingsubscriber and the connection to be released, all in themanner described indetail hereinafter. As suming that the called line is idle, the operator again operates the dial key 403 to cause the re- :operation of the two relays R420 .and R430 .so that the :pulsing springs of the calling device .404 are againincluded in the circuit {or energizing theline relay-R150. After performing this operation,the operator may dial the digits of the code designating the desired called substation C. In this regard, .it-is pointed out that ringing current is projected over the selected side of the selected called line in response to operation of the calling device.41l4v and, further, the length of each period during which ringing current is transmitted over the called ;line is determined by the dialed to produce a short ring at the called substation and a ringing ,digit of eight impulses may of the line, thereby to prevent the line relay from responding to ringing current projected over the line and to clear the line of the impedance represented by the operating winding Of this relay. At RA212, the relay R210 opens a oint in the above-traced circuits by way of, which busy tone current is transmitted to the calling substation and to the operators position 25. At RA213 and RA216, the relay R210 disconnects the link line conductors C180 and C180 from the link line conductors C348 and C341, whereby, if the called line 11 is occupied with a reverting call, the calling subscriber is prevented from listenin to the conversation being held over this line. .At

RA213 and RA215 and their respective associated working contacts, the relayR210 connects the conductors a and b of the called line 11 to the link line conductors C348 and C341, respectively, whereby the calling operator may, .upon

restoring the dial key .403 to normal, monitor the called line for the purpose of determining whether or not this line is occupied with a .reverting call. At RA214, the relay R210 opens ,a point in the previously traced pulsing circuit extending to the two relays R210 and R215 and prepares a circuit, traced hereinafter, for energizing the relay R240. At RA215, the relay R210 opens a point in the above-traced operatingcircuit for the relay R220. At RA215, the relay R2 I 0 prepares the circuit for energizing the relay R250. At RA211, the relay R210 disconnects the link line conductor C188 from ground. At RAZ 18, the relay R210 opens a point in the previously traced operating circuit for the digit transfer relay R230. an alternative circuit, traced hereinafter, for energizing the signal control relay R145. Finally, at RA219', the relay R210 opens a further point in the circuit for energizing the magnet 290 of the connector switch during the release of the link.

As explained above, after dialing the line ,selecting digits and the digit designating the side of the line over which ringing current is to ,be

projected, the operator attending the position 25.

At RA219, the relay R210 prepares be dialed to produce a long ring at the called substation. Assuming that the code designating the desired substation C is one long andone short, the operator first dials a digit of eight impulses. The line relay R responds to the impulses of this digit in the manner previously explained. When the relay.R150 restores at the beginning of the first impulse of the digit, it recompletes, at,RA1- 5.1 the previously traced circuit for energizingthe relay R110. ,A branch of this circuit may be traced as extending from ground by way of RAIN, RA15.1, RA1-65, C134, RA202,

RA214, ,RA234 and. the winding of R240 to battery. The relayR240, upon operating, completes, at its armature .241 and the respective associated working contact, a circuit extending from ground at RA23B for energizing the slow-to-release relay R245. The resulting operation of the last-mentioned relay is without effect at this time. The relay R110, .upon operating at the beginning of the first impulse of the digit, further prepares,.at

,RA113, the previously mentioned circuitfor energizing the relay R250. This circuit is completed in response to the reoperation of the relay R150 at the end of the open circuit period of theflfirst impulse and extends from ,ground at RA164 by way of .RA151, RA1.13, C180, RA2I5' and the lower winding of R250 to battery. When energized over this circuit, the relay R250 operates to complete, at RA251, an obvious path for shortcircuiting its upper Winding, thereby to render itself slow to release. At RA252, the relay R250 completes an obvious circuit for energizing the relay R260. The relay R260, upon operating, completes, at RA202, the above-mentioned circuit for projecting ringing current over the positive side of the selected line 1 1. This circuit extends from the ungrounded terminal of the secondary winding of the transformer 392 by way of C206,

mains operated until the train of impulses is ended. Accordingly, the relay R260 is held in its operated position for the duration of v the first ringing digit. Since this digit comprises eight impulses, the ringer provided at the called substation and the other ringers connected between the positive side of the line I I and ground, are energized for a relatively long time interval.

When the relay R260 operates at the beginning of the first ringing digit, itinterrupts, atlO RA263, the previously tracedholdingcircuit for the digit transfer'relay R230. At RA264-, the relay R260 opens a point in the above-mentioned alternative circuit for energizing the signal control relay RI45.- The relay R230; upon restor- "f5 ing, opens, at RA23I, a point in the previously traced circuits for transmitting busy tone current to the calling substation and to the operators position 25. AtRA233, the-relay R230 opens a furtherpoint in the previously traced zopulsing circuit extending to the two relays R210 and R215 and reprepares a point'in the pulsing ,circuit extendingthrough the winding of the magnet 290; At-RA235, the relay R230 opens the path short-circuiting the lower winding of 25 the relay R220. At RA236, the relay R230 opens the previously tracedoperating circuit for the slow-to-release relay R245, causing the lastmentioned relay to restore. At RA234, the relayR230 interrupts the above-traced operating s'o in its own holding circuit: At RA238, the relay R230 reprepares the path for'impressing ground potential upon the all-links-busy conductor C343. At RA238, the relay R230 prepares a point in the previously'inentioned circuit for energizing the magnet 290 during the release of the link 30. At its armatures RA232and RA231, the relay R230 connects the link line conductors CI80 and CI88 to the link line conductors CI19 and CI89 and, in so doing, completes a circuit for transmitting a portion of the ringing'current'45 by way of the calling line for the purpose; of producing the usual ring-back tone signal at the calling substation. The path'traversed bythis current may, in the present case, beitraced as extending from the ungrounded terminal 'of the secondary winding of the transformer 392 by way of C296, RA219, RA262, the condenser'2'62", RA231, CI88, the winding I I4, the condenser 'I I9,

the winding H3, CI80, RA232, the condenser 26], RA26I and RA216 tothe grounded terminal of the indicated transformer winding. Due to the alternating character of this'icurrent, a corresponding current is transmitted by induction to the loop circuit extending to the calling substation to be reproduced by the receiver pro-= vided at this substation.

At the end of the first ringing digit, the relay RI50 is held operated for a time interval sufii- I "cient to permit the release of the relays Rl 'iil,

R250 and R260 in the order named; The last- At these same armaturesthe relay R260 disconnects the link line'conductors CI80 and Cl88 from the ringing ,ourrent source, thereby to terminate the ring-back tone signal. At RA263,

the relay R260 -reprepares the ,holdingl circuit for the digit-transfer relay R230. Finally, at

RA264, the relay R260 reprepares the abovementioned alternative operating circuit for the signal control relay RI45. During the second and each succeeding ringing digit dialed at the operators position 25, the relays RI10, R250 and R260 respond, in the exact manner just described, to cause ringing current to be projected over the selected side of the selected called line for a period determined by the numerical value of the digit dialed. During the succeeding ringing digits, the relays R230, R240 and R245 are not affected, since the relay R230 occupies its restored position. Obviously, by repeatedlyoperating the calling device 404, the operator may -RA26I and RA216 to the grounded terminal of the secondary winding of the transformerw392.

As explained above, in order to energize the ringer provided at a called substation and connected between the negative line conductor of "the line and ground, the first digit dialed at the Y operators position following the two line select- -ing digits is such that the relay R215 is not caused -to operate. Acocordingly,-when the ringing digits are dialed, ringing current is transmitted over a path which extends from the un- I grounded terminal of the indicated transformer secondary winding by way of C296, RA216,

RA26I, RA2I3, the wiper 286, the negative conductor of the selected-line and through the series connected ringer and condenser provided at the called substation to the grounded terminal of the ringing-current source.

After ringing the called substation one or more times, the operator may restore the dial key 403 to normal to cause the restoration of the relays R420 and R430 and the reoperation of the relay R450 and thus recomplete the signaling channel between her telephone set and the called line. When this channel is completed, the operator may monitor the connection to determinewhen and if the call is answered. If the call is not answered within a reasonable time interval, the

operator may again actuate the dial key 403 to its oil-normal position and operate the calling device 404 to rering the called substation. When the call is answered, the desired talking circuit is completed between'the calling and called substations. Thebranch of this'circuit extending to the calling substation A is obvious. The'branch of the talking circuit which extends to the called substation C may partially be traced as extending by way of the line conductor Ila, the Wiper 286, RA2I3, RA26I, RA232, CI80, the winding H3, the condenser H9, the winding H4, CI88, RA231, RA262, RA2I6, the wiper 288 and the line conductor b. The branch of this talking circuit'over which the'operator may monitor the connection may partially be traced as extending from the negative link line conductor CI by way of RA232, CH9, RAI62, C348, the repeater windings 394 and 395, the condenser 395', C341, RAI61, RAI14, CI89 and RA231 to the positive link line conductor CI88. Assuming that the calling and called substations are of the local 

